1. Field of the Description
The present description relates, in general, to designs for omniwheels and omnidirectional vehicles (or other omnidirectional devices), and, more particularly, to a wheel assembly with multi-sphere omniwheels (e.g., two or more spherically shaped rollers or “sub-wheels” make up each omniwheel of the wheel assembly) that can be used in any omnidirectional device such as an omnidirectional vehicle for use in an amusement park ride or omnidirectional apparatus for moving objects over both smooth and rough or contoured surfaces, which can be problematic for conventional omniwheels to smoothly traverse.
2. Relevant Background
Omniwheels (or omnidirectional wheels, poly wheels, or the like) have been in use for many years and are often employed in holonomic drive systems. Well-known omniwheels are wheels with small discs or rollers around the circumference or rim of a larger wheel (or the omniwheel hub), and small discs or rollers provide the contact surface for the omniwheel and are arranged, typically, to be perpendicular to the turning direction. The effect is that the omniwheel can be driven with full force by rotating a shaft along the major axis of the omniwheel while still being able to slide laterally via free or undriven rotation of the small discs or rollers about their minor axes.
In general, omnidirectional wheels or omniwheels allow movements of a supported vehicle or object in all directions (i.e., forward/backward, sideways, and spin) freely and immediately. In particular, omnidirection wheels allow a vehicle or supported object to move sideways without the intermediate maneuvers that are need for “parallel parking” a vehicle with conventional wheels. Mathematically, omniwheels are holonomic wheels while conventional wheels are nonholonomic. As noted above, omniwheels generally include a large wheel or hub that is rimmed with smaller rollers around the circumference, and the rollers are set perpendicularly to the major axis of the large wheel or hub. In forward/backward motions, the large wheel or hub rotates about the major axis and presents a large diameter with minimal friction and the ability to overcome obstacles such as bumps on a surface. In sideways motions, the typically much smaller rollers present a smaller diameter than the large wheel or hub and, as a result, often are unable to overcome obstacles including relatively small bumps in a surface over which the omniwheel is rolling. Effectively, traditional omniwheels are asymmetric as the ratio of the largest diameter (e.g., of the main/large wheel or hub) to the smallest diameter (e.g., of the smaller roller) determines the uniformity.
A design challenge arises when it is desired to provide a wheel (and suspension in many cases) system that can allow a vehicle or object supported by the wheel system to move in all directions over a bumpy surface. Traditional wheels (not omniwheels) can overcome bumps on a surface with ease, and currently available omniwheels can move in all directions. However, the combination of these two capabilities has not yet been effectively achieved as currently available omniwheels cannot overcome bumps in all directions (e.g., rolling or sliding on the smaller rollers is not effective on a surface with any significant bumps. Also, conventional omniwheels tend to be relatively complex to fabricate and control/drive and often do not provide a smooth contact surface (e.g., due to spaces between the smaller rollers on the circumference or rim of the larger wheel).
FIGS. 1-6 illustrate examples of currently available omniwheels, and each is useful for providing multidirectional movement on a smooth, flat surface but can have problems on a bumpy or rough surface. FIG. 1 illustrates an omnidirectional wheel 100 with a main/larger wheel or hub 110 with a center hole or opening 115 to allow the omnidirectional wheel 100 to be attached to a drive shaft or axle (not shown) for driving the omnidirectional wheel to rotate about the major axis, AxisMajor, of the larger wheel or hub 110. A plurality of smaller rollers 120 (e.g., fourteen rollers) are provided in a spaced apart arrangement about the circumference (or outer rim) of the larger wheel/hub 110. The rollers 120 provide a contact surface for the omnidirectional wheel 110 (i.e., traditional omniwheels are designed to provide a single contact point) and rotate about an axis, AxisMinor, that is in a plane perpendicular to the rotation axis, AxisMajor, of the larger wheel/hub 110. It should be understood that rollers 120 are sized to have a diameter that is much smaller than the diameter of the larger wheel/hub 110. Obstacles that can be successfully forded in the sideways direction (parallel to the main rotation axis, AxisMajor) are, therefore, much smaller than the ones that can be overcome in the forward direction during rotation of the larger wheel/hub 110. This can significantly decrease the usability of the omniwheel 100 on rough or bumpy surfaces or to overcome surface obstacles.
FIG. 2 illustrates an omniwheel 200 made up of a set of three side-by-side larger wheels/hubs 210 with holes/openings 215 for a draft shaft (not shown) for driving the larger wheels/hubs 210 to rotate about a rotation axis, AxisMajor. Each of the wheels/hubs 210 includes a number of rollers 220 on their outer rim, and each of the rollers 220 is configured to rotate freely about an axis, AxisMinor, that is in a plane perpendicular to the rotation axis, AxisMajor, of the larger wheel/hub 210. The wheels/hubs 210 are arranged so that their rollers 220 are offset from each other (e.g., the rollers 220 are provided in multiple layers to provide a more continuous contact surface). FIG. 3 also presents an omniwheel 300 with a hub/larger wheel 310 with a center hole 315 to allow it to be rotated by a shaft/axle (not shown) about its rotation axis, AxisMajor. A number of layered and offset rollers 320 are provided about the outer rim of the larger wheel/hub 310 and each rotates about a longitudinal axis, AxisMinor, of the roller 320. In each of the omnidirectional wheels 200 and 300, the diameters of the rollers 220 and 320 has to be much smaller than the diameter of the larger wheel/hubs 210 and 310.
FIG. 4 illustrates another design for an omniwheel 400 that includes a larger wheel or hub 410 with a central hole/opening 415 to allow the hub 410 to be affixed to a drive shaft (not shown) to rotate/drive the omniwheel about the main rotation axis, AxisMajor, passing through the opening/hole 415. Further, a plurality of overlapping rollers 420 and 425 are provided on the circumferential surface or rim of the larger wheel or hub 410 and each is adapted to rotate about its longitudinal axis, AxisMinor, which each are in a plane that is perpendicular to the main rotation axis, AxisMajor, of the omniwheel 400. The omniwheel 400 may be considered an extra-smooth omniwheel that more accurately approximates the shape of a circular wheel with its contact surfaces provided (one at a time) by the rollers 420 and 425. To keep a single layer, this design necessarily has small diameter rollers 425 and larger diameter rollers 420, and the ability to ford or overcome bumps or obstacles is limited by the smaller diameter of the rollers 425.
FIGS. 5A and 5B show top and side views, respectively, of a spherically-shaped omniwheel 500 which is supported and can be driven by shaft 516 to rotate about an axis, AxisMajor. Two sphere halves 520 are mounted on shaft 516 and rotate about an axis, AxisMinor, that is perpendicular to the major rotation axis, AxisMajor. At each spaced apart end of the sphere halves 520, smaller diameter rollers 525 are provided and mounted to rotate about an axis, AxisMinor2, that is perpendicular to both the major rotation axis, AxisMajor, and the first minor axis, AxisMinor1. In the omniwheel 500, the large diameter rollers 520 have become as large as the diameter of the omniwheel 500. In balance, the small diameter rollers 525 have become tiny or much, much smaller than the diameter of the omniwheel 500, and, as a result, the design looks like it would be smoother than many other designs. However, when the smaller rollers 525 hit obstacles, even the smallest obstacles (smallest dips or bumps in a surface) may undesirably stop the rolling of the omniwheel 500.
FIG. 6 shows another design for an omnidirectional wheel 600 with a larger wheel or hub 610 that can be driven to rotate about its rotation axis, AxisMajor. About the peripheral surface or rim of this larger wheel or hub 610, a plurality of free-rotating rollers 620 are provided that each rotates about its longitudinal axis, AxisMinor. In the omnidirectional wheel 600, the smaller diameter rollers 620 are positioned at 45 degree angles rather than in the plane of the hub 610. This allows a torque applied about the driven hub axis, AxisMajor, to create ground forces outside the plane of the hub, and a vehicle supported by multiple parallel wheels 600 can be actively driven sideways relative to the wheels. However, the small diameter of the rollers 620 accentuates the asymmetry of the omniwheel 600 making it unsuited for many bumpy surfaces or for fording many obstacles that may be on a surface.
Hence, there remains a need for an improved omniwheel or omniwheel assembly providing two or more omniwheels that provides a more smooth contact surface (or “ride”), is less complex to fabricate and control/drive, and, significantly, is able to move easily in all directions on both smooth and bumpy/rough surfaces. Preferably such omniwheels or omniwheel assemblies would be adapted for use in “all-terrain” omnidirectional devices (e.g., omnidirectional vehicles) that more easily overcome obstacles or bumps on a surface. Since the omniwheels preferably are more simple in design, fabrication, and use than existing omniwheels, it is likely that the new omniwheels will be more robust and more useful in less controlled environments such that the new omniwheels will find application in a large variety of domains beyond robots such as in omnidirectional vehicles (for amusement park rides and other applications/environments).